Surprisingly enough, there is no actual difference between hair and fur. Though unique to mammals, they are chemically indistinguishable and are made of keratin, giving them the same chemical make-up as skin, feathers, and nails.
The purpose of hair and fur seems to be the same, no matter the host. Many animals couldn't live without its insulating qualities, and many humans appreciate a warmer head, thanks to their hair. Often, hair serves as protection against injury. An excellent example of this is the thick coat of fur around a lion's neck. This mane will make it very difficult for his enemies to wound him, especially as big cats and other carnivores often go for the throat when hunting. In addition to this, fur can further serve to carry a scent that can vary in purpose from species to species. Although much of the hair that grows on human bodies seems unnecessary, most believe that it has slowly decreased over time, along with humans' need for it.
The primary difference between hair and fur, it turns out, is word usage. People generally refer to non-human mammals as having fur, while humans are said to have hair, but there are a few exceptions. When an animal has very coarse or sparse fur, as in the case of a pig or elephant, people usually call it hair. Similarly, a cat or other animal without fur is referred to as "hairless" or even "naked."
On the other hand, people sometimes apply the term fur to ourselves. “He has a hairy chest,” could also be “He has a furry chest.” Generally, however, fur applies to mammals other than humans, unless someone is making a deliberate attempt to apply animal characteristics to humans.
Most people are also convinced that the two are different because fur tends to grow to a set length. The truth is, in every mammal, hair growth is determined by genetic make-up. So a shorthaired cat doesn’t suddenly become a longhaired cat if it doesn’t get a haircut.
Hair or fur length can also be genetically determined within the variety of humans. Not everyone can grow his or her hair long with equal facility — many women have tried and failed to grow their hair long. Facial hair is also varied, with some men having a lot, and some very little. Genetics tends to be the primary factor.
People also make the distinction between hair and fur when discussing animal pelts. For the most part, the pelts of animals are called furs, as in a fur coat, fur trim, etc. A few exceptions in the distinction for mammals occurs here also. For example, mohair is harvested from the alpaca and woven into sweaters and the like, and angora is combed from the angora rabbit and also used in soft sweaters. Often, these are both considered hair.